Being as I did the '33 Zenith, I'll post up what I'm doing with the radio set here. The car has been converted to 12 Volts from 6; I decided to keep with that because finding 6V stuff is awkward when you're on the road and need a repair. I didn't want to run the radio through a dropper circuit, those are wasteful and get hot; down here I don't need 2 sources of heat in the car if the radio is on. So, having purchased a 6V 1951 radio with the correct buttons and knobs to match the car's interior (deluxe), I bought a 1956 Buick radio, which is similar but natively 12V. Not similar enough to do a straight swap, but with enough parts inside common to make a sort of Frankenstein's Monster of a radio. Phil
This was the radio as I received it. It had been in damp-ish storage for many years. The innards weren't too bad but one thing was a problem- the tuning coils were all out of alignment. Turned out that the pot-metal frame the coils sat in had zinc pest and was falling apart. Cheap metal, damp climate. Lead impurity. The metal turns to the consistency of shortcrust pastry and quite literally falls apart after swelling up to about 115% its original size. So, I cleaned the rest of it up and set about looking at eBay. --Phil
Enter a 1956 Buick Sonomatic! Same kind of idea as the Pontiac radio but 12V. The usual electronic and chassis recycling going on. The Sonomatic set did work (albeit half-way because one of the tubes was broken in the output stage) so that was a good start. I got as far as gutting the transformer, removing the old electrolytic cap from inside and putting it into the chassis, along with the new vibrator base. Then I transferred the tuner frame to the 1951 chassis. At that point we left town to go to New York state for a friend's wedding, I came back and started on the Zenith... and that's where it ended. Until now.
I figured out what was what and how it was internally wired and re-drew the power supply schematic as it needs to be. Getting somewhere now. I need to order me some parts! Phil
Radio restoration & repair is kind of fun. I did about 40 or 50, that I sniped off ePay or yard sales, showed up at my door, friends wanting to get Grandma's kitchen radio working again. The big wooden radio consoles are pretty cool too. Every one responded nicely to fresh electrolytic power supply capacitors, coupling and bypass capacitors, and maybe a few resistors. Then give it a good alignment. A lot like firing up an engine that hasn't ran in decades. I haven't messed with car radios.
This is really impressive, but do you like the stuff on the airwaves today on AM? Sent from my SM-T350 using The H.A.M.B. mobile app
Not all of it. So, this is gonna get a slight modification to allow me to switch the AM over to an external source. Also has the effect of making it significantly better quality audio. The limiting factor is the output transformer and loudspeaker. Phil
Alrighty, hopefully the last revision of the circuit. Forgot that the power stage is not 6V6 tubes, so the correct pinouts and tube substitution are now noted. Phil
Right, but they are cramped! Not like the football field sized cavern of an old Zenith. The one exception is Philco, they used proprietary tar encased coupling and bypass capacitors. I don't like those. And wrapped their coils - oscillator, mixer, antenna, in cellophane. It turns to goo and dissolved the magnet wire. I rewound all three coils. It worked great when I was done, but if I would have charged the guy by the hours I had in it he would have choked. There isn't much to listen to on the AM band during the day. At night, it gets pretty interesting. To me it's part of the deal. I have thousands of tunes available on my fricking phone. But I want an original AM radio in the dash to work as advertised, tubes and everything. It just has to. Gutting the innards and installing some POS is just dirty pool, there's no need to do that anymore.
Yeah, it's a bit of a squeeze but no worse than an old farm radio. Agreed on the hours. I didn't charge my friend labor on the Zenith I just redid; it was $202 and change in parts. That's the bill he got. It was done for enjoyment on my part too, and as an ex-Marine he deserves that at least. But on the stations front, there's a few flamethrowers that I can pick up around here during the day but AM as a nighttime band is good- I can pick up WSM here on a good night. Plus, there's nothing wrong with a decent tube set (power consumption notwithstanding) because this one came from the pinnacle of AM radio just before FM started to get a foot in the door. Wartime radio development coupled with more modern component parts- but just before miniature tubes started to hit the market. It's even got a halfway decent output transformer in it. Phil
Got my bench set up, ready to go. Calibrated everything, got my RF and sig gen sets, VTVM et al. Waiting on parts now. Phil
I even like to use vintage solder - Kester. Get a whiff of that old timey rosin flux, it smells like maybe pine or something?
We used to cram 20oz 6x9 Utahs into those. Sometimes we had to stand on the cases to get the screws started back in ! Of course, that was a long, long time ago, in $75 Buicks, Cads, & Olds ….
Yeah, this stuff isn't quite as strong as the old reel I used to have. Know exactly what you mean, though! Phil
It's still an option but I wanted to keep the feel of the original; the wait for it to warm up, the buzzing crackle as the B voltage starts to reach threshold of the tubes starting to work. I started to pull solder joints apart last night. Started on the power supply side. I had previously repaired the vibrator socket, and the center pin tang decided to break off. Glad it did now and not in use; that would have been horrible to try and diagnose. Those sockets are difficult to find (3-pin). If it all goes south I'll get a 4-pin one because they're much more standard and available, and retrofit that. It originally had a 4-pin, the 3 came from the '56 set. Phil
What was the current draw on something like that, when working as advertised? Are you converting the vibrator to solid state?
If I can't get that socket to work correctly, I likely will. The solid state ones work at a higher frequency and cause a higher-pitch whine than the mechanical ones so need additional filtering. However, the 12V vibrator I have works well so I was going to try use it. The current draw is 3.8 Amps at 12V. The set is rated at about 45 Watts. The Buick set is about 40 Watts, it has one less tube. --Phil
4 amps? Jeeze, doubles as a Hot Pocket warmer on road trips. What did the 6 volt version draw I wonder.
The tang for the ground lug decided to break off, so I split the 2 phenolic pieces apart, made a new lug from a fork connector and soldered that down to the chassis with a gas torch to get good adhesion. From there, I put the broken piece in place and used a smaller heat source to solder it after bending it down to line up. Supported from behind as it's pushed in, the vibrator connects nicely. It's supported once it's in on the other side by a 6-finger spring clip. I connected it up and put a 9v square battery on the input. The output pegged my meter set to 1500 VAC. (No capacitors in the circuit yet). Bueno. Phil
Dissecting the volume and tone controls tonight led to an interesting discovery; the volume potentiometer is 25/75% tapped and that means there can be different capacitance on one side of the scale to the other. Net result? Linear tone alteration- the lower the volume, the more bass and treble you get. Accounts for the speaker and hearing characteristics- it's got automatic loudness compensation. That's pretty sharp for a car radio. Spent the rest of the time re-familiarizing myself with the circuit and schematic. I think this should be a fun (and hopefully satisfying) rebuild. One thing I didn't do was check the output transformer for continuity. Tomorrow. I do have a working spare, somewhere. Phil
14C5 power output tubes arrived. The parts that I need to be able to start on the radio are still in New Orleans and won't be here until at least tomorrow. Phil
High tension power supply rebuilt and tested. A half dead 9V battery gives us a half-way decent B+ of about 140VDC (meter showing about 90 there). So far so good Phil
The Jalopy Journal
